The present invention relates to hot plate presses and, more particularly, to hot plate presses which are operated entirely by hydraulic machinery.
Hot plate presses, also known as injection molding presses, typically consist of a single base on which is mounted a hydraulic pump, a reservoir of hydraulic fluid, and the press itself. The press consists of a stationary upper hot plate adapted to support a mold half, a lower hot plate mounted on a vertically movable platen and adapted to support a complementary mold half, and injection molding equipment connected to the upper hot plate.
The complementary mold half of the lower hot plate is moved upwardly by lifting cylinders to engage the upper mold half, and the mold halves are clamped together by a clamping cylinder which urges the movable lower platen upwardly toward the fixed upper platen. In one embodiment of such a hydraulic press, the movable lower platen includes a vertically oriented post which slides in and out of a hole formed in the base of the press as the lifting cylinders move the platen upwardly or downwardly. To lock the platen in an upward position, the lifting cylinders lift the platen upwardly until the post is withdrawn completely from the hole, then a hydraulic rotary actuator is activated to pivot a plate which covers the hole. The platen is then urged downward until the post rests on top of the plate. The clamping cylinder is then actuated to clamp the mold halves together and the injection step can then be initiated.
The injection molding equipment includes a hydraulically operated screw conveyor positioned within a heated chamber for receiving the material to be injected into the mold, and an injection cylinder communicating with the heated screw. The injection cylinder typically is vertically oriented and includes a ram connected to a hydraulic cylinder. In operation, the hydraulic screw receives a charge of material such as plastic or rubber, heats the material to plasticize it, then conveys material by the screw conveyor to the injection cylinder. The flow of material into the cylinder causes the ram to move upwardly and evacuate fluid from the portion of the injection cylinder above the piston connected to the ram. Once a charge of plasticized material has been received, the injection cylinder is actuated and the piston drives the ram downwardly to force the plasticized material through a sprue and into the mold cavity formed by the clamped upper and lower mold halves.
All of the components previously described are often powered by pressurized hydraulic fluid which is conveyed from a motor-driven pump mounted on the base. With such systems, the output of the pump is conveyed by a rigid conduit to a valve manifold or valve plate. The valve manifold is mounted on the base and is spaced from the press itself, typically interposed between the reservoir and pump assembly and the press. The valve manifold supports all of the valves which actuate the hydraulic components of the press, and may include internal or enclosed conduits which connect the valves to the hydraulic supply line from the pump and to the return line to the reservoir. The valves are also connected by means of flexible hoses to their corresponding hydraulic components on the press.
A disadvantage with hot presses of this type is that the presence of a valve manifold between the hydraulic press components and the pump and reservoir components requires additional space on the base and hence increases the overall dimensions of the press. Another disadvantage is that the valves of the valve manifold communicate with their corresponding hydraulic components by flexible hoses, each of which has a useful life which is substantially less than a corresponding length of rigid hose made of metal. Furthermore, these lengths of hose must be relatively long and must be fitted about the side plates on side structure of the press.
Accordingly, there is a need for a hydraulically operated hot press in which the overall dimensions of the base supporting the press are held to a minimum. Furthermore, there is a need for a hydraulic press in which the distance between the hydraulic valves and their corresponding hydraulic components is held to a minimum, thereby minimizing the number and lengths of flexible hose required.